What reasons should an app have to need my phone's International Mobile Equipment Identity number? I noticed that unreasonably many of ordinary apps have the "phone state and identity" permission. For example, Remember the Milk. What do they ask it for? Am I insufficiently paranoid?

It's often used to identify the unique phone, but often this is actually quite a bad idea. Most apps would be better off identifying you as a user, who can use multiple different devices on one account.